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#82122 - 10/17/02 08:12 PM Another stupid ampacity question  
elecbob  Offline
Joined: Aug 2002
Posts: 141
I routinely fuse #8 copper at 40 amps. Table 310-16 says #8 THHN is good for 50 amps. A customer is replacing an existing spa with a spa with a 30 amp 240 v GFI and a 20 amp 120 v GFI. The disconnect box is fed with 4#8 CU conductors from a 50 amp CB in the main panel about 90 feet away. Do I need to replace the #8 CU with #6 CU?

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#82123 - 10/17/02 08:29 PM Re: Another stupid ampacity question  
HotLine1  Offline

Joined: Apr 2002
Posts: 6,853
Brick, NJ USA
I don't fully understand your question.
Is the spa 240 volt, 3 wire (hot/hot/neut/grd) or 2 wire (hot/hot/grd)??

How does the 120 volt GFi "fit-in"?? If you "tap it off" of the 50 amp feeder, how are you protecting it?? (OCP)

The prime answer is "yes" you can protect 8 THHN Cu at 50 amps per NEC 310-16, before you do any de-rating, if required.

The above is my humble opinion.


#82124 - 10/17/02 09:02 PM Re: Another stupid ampacity question  
caselec  Offline
Joined: Apr 2002
Posts: 558
San Jose, CA

#8 THHN is rated for 50 amps if all of the terminals it is connected to are rated for 75C. If the terminal are not marked with a temperature rating or only rated for 60C then #8 is only good for 40 amps so #6 would need to be used.


Curt Swartz

#82125 - 10/17/02 11:43 PM Re: Another stupid ampacity question  
sparky  Offline
Joined: Oct 2000
Posts: 5,311
not a stupid Q at all considering the varied interactive formats for derating scattered thru the NEC

#82126 - 10/18/02 12:01 AM Re: Another stupid ampacity question  
elecbob  Offline
Joined: Aug 2002
Posts: 141
There is a 30 amp 2 pole (240 volt) GFI for the heating elements and a 20 amp single pole (120 volt) GFI breaker for the motor. I would be pulling 3#10 (black, red and green)wires and 2#12 (black and white) wires from the GFI breakers to the spa.
I often wonder what the energy cost per hour spent using these things is. I guess ours is not to wonder why. Ours is but to make money hooking up the damn things.

#82127 - 10/18/02 12:05 PM Re: Another stupid ampacity question  
HotLine1  Offline

Joined: Apr 2002
Posts: 6,853
Brick, NJ USA
Didn't put the derating thing in my post to you, sorry.
The cost would be approx.
240x30=7200 watts
1 HP motor= 750 watts
total max of 7950 watts or 8 KW rounded max
At 12cents per KWHr, a whopping calculated 96 cents.
Actual costs will vary based on the local utility rates, and service charges that are added to the monthly billing.

The above disclaimer is for 66wv.


#82128 - 10/19/02 03:01 AM Re: Another stupid ampacity question  
sparky66wv  Offline
Joined: Nov 2000
Posts: 2,236
West Virginia
LOL! Hee hee!

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Hey, ya always gotta give yerself an "out", just in case!

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